New research hints at a more complicated picture. A recent study looking at the effect of carbohydrate consumption on glycemic index couldn’t detect a difference between the PPGRs of sourdough and white breads among their 20 subjects.2 That itself is a curious result that flies in the face of a lot of what we thought we knew about sourdough’s health benefits. However, with only 20 subjects it’s possible that the study was a little underpowered. 

But what’s truly interesting about this study is that for several of the volunteers the sourdough actually had a substantially higher glycemic index than the white bread. 

Further, the paper goes on to point out, each subject’s relative response to the different breads depended on the composition of his or her individual gut microbiome — the complex ecosystem of bacteria that lives in our guts. 

The authors make a fairly radical claim, which will need larger studies to confirm, that everyone has a different glycemic-index response for each type of bread. Suddenly the idea that sourdough is better for you might depend on who you are. 

“You,” of course, refers to a lean, mean fighting machine, honed to razor-edge metabolic efficiency by tens of thousands of years of evolutionary challenge. Right? Yeah, sure. The sourdough mafia would have us believe that evolution has left us better equipped to metabolize breads such as sourdough than more processed breads. 

But at best, humans have been eating bread resembling sourdough for only a few thousand years3 — a blink of an eye in evolutionary terms. Logic demands that we look elsewhere to explain why some studies purport to show that our bodies process sourdough more smoothly than other breads.4

So, while sourdough may indeed be enjoying a renaissance, we should still take claims of its metabolic superiority with a grain of salt. Or better yet, with a schmear of cream cheese. 

There is one thing we can all agree on, though. It tastes damn good.

Reference

  1. Najjar AM, et al. “The Acute Impact of Ingestion of Breads of Varying Composition on Blood Glucose, Insulin and Incretins Following First and Second Meals.” British Journal of Nutrition. 2008;101(3): 391-398.
  2. Korem T, et al. “Bread Affects Clinical Parameters and Induces Gut Microbiome-Associated Personal Glycemic Responses.” Cell Metabolism. 2017;25(6): 1243-1253.
  3. Griggs B. “The Rise and Rise of Sourdough Bread.” The Guardian. Updated August 12, 2014. Available at: https://www.theguardian.com/lifeandstyle/2014/aug/12/rise-sourdough-bread-slow-fermented-health-benefits. Accessed June 19, 2017.
  4. Maioli M, et al. “Sourdough-Leavened Bread Improves Postprandial Glucose and Insulin Plasma Levels in Subjects With Impaired Glucose Tolerance.” Acta Diabetologica. 2008;45(2): 91-96.

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